Heal thyself: The 'bio-inspired' materials that self-repair

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Photos:The emerging world of self-healing materials

The emerging world of self-healing materials – An optical microscope image of a self-healing polymer, with microcapsules containing a red healing agent embedded in the material.

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Photos:The emerging world of self-healing materials

The emerging world of self-healing materials – Optical microscope image of a self-healing polymer in action, as microcapsules containing a red healing agent begin to rupture as a crack progresses through the material.

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Photos:The emerging world of self-healing materials

The emerging world of self-healing materials – This image, taken using a scanning electron microscope, shows a ruptured microcapsule contained in a self-healing epoxy.

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Story highlights

Materials which heal themselves when damaged are expected to hit the market in 2013

Some of these "bio-inspired" materials use a model based on veins to release healing agents

They have potential to lengthen the the lifetime of products and reduce demand on raw materials

Self-healing coatings to protect marine structures from corrosion will be released this year

The notion of self-healing materials might seem beamed in straight from the plot of one of the "Terminator" movies -- but the first versions of this technology are destined to hit the market this year.

While liquid metals that can mesh back together after taking a shotgun blast remain the stuff of science fiction for now, simpler models -- such as anti-corrosion coatings that repair themselves after being damaged -- have already become a reality.

The potential of this new field of innovation to extend the lifetime and safety of products, reduce demand for raw construction materials, and allow machines in remote or inaccessible locations to stay operative has excited organizations such as the World Economic Forum, which earlier this month named it one of the top emerging technologies.

U.S. firm Autonomic Materials has been working on developing self-healing coatings, sealants and adhesives based on microcapsule technologies devised by the University of Illinois at Urbana-Champaign, which have been demonstrated to be able to allow electrical circuits to repair themselves.

Chief executive Joe Giuliani said the initial applications brought to market would be in self-healing coatings used on marine assets such as ships, docks or oil and gas platforms to protect the metal beneath from corrosion.

Coatings were often damaged by impact when the structures were moved or being installed, or through collision with other bodies in the water.

Giuliani said the technology was based on a system whereby two different microcapsules were incorporated into the coating, one containing the self-healing component and the other containing a catalyst. When the coating was damaged, the microcapsules would rupture and the contents would react with each other, healing the damage to restore the integrity of the coating.

"When damage occurs, they go to the site of the damage and can actually heal underwater without the presence of oxygen," he said.

He said the technology provided a benefit by extending the periods at which maintenance had to be carried out, and reducing the damage it sustained, extending the life of the structure.

Reducing maintenance periods was immensely valuable for owners of oil rigs and similar structures, which were often situated in remote locations and extremely costly to take out of commission for maintenance, he said. Corrosion is estimated to cost $500 billion worldwide each year.

"This is not an aesthetic fix, this is purely functional. This is for when people want to provide corrosion protection to their metal assets."

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While the microcapsule coatings will be the first self-healing product to make it to market, scientists are also working on developing more complex models.

Professor Ian Bond, head of the aerospace engineering department at the UK's University of Bristol, said his team had been developing a "bio-inspired" vascular system, based on the veins in the human body.

The technology could potentially be used in the high-performance composite polymer materials replacing metal in the new generation of superjumbo aircraft.

A simple model of the "bio-inspired" technology used hollow fibers containing liquids that would leak out and repair damage on impact.

Bond says this model had a shortcoming though, in that once the healing agent was used, it couldn't be replenished.

To resolve this, researchers were focusing on developing a vascular system in which liquid could be circulated in a network of hollow fibers within the material, which would allow the healing agent to be restocked through an access point.

The team has made the technology work in laboratory settings but there are a number of challenges in applying it to real-life settings. One issue is that the vascular networks could become blocked once damage was sustained and the "veins" were ruptured -- a potential solution for which was to build multiple pathways for the liquid to circulate.

Developing a substance that would work reliably in potentially extreme conditions and remain stable over the life of the material was also a challenge.

"They are hard criteria to meet because they're invariably reactive components which have a tendency to want to change," Bond said.

The self-healing technologies did not restore the material to its pristine state -- "There is some residual damage," he said.

The high standards of product testing required for the aerospace industry meant that the self-healing composites were not likely to be found in airplane construction any time soon. But he expected they could start appearing in offshore wind turbines within 5-10 years.

Other avenues being explored were materials that would "bruise" to show the site of damage -- that has potential applications in car construction -- and glass that repaired itself by flooding the cracks with liquid when it shattered.

"The cracks will disappear but you wouldn't restore the structural integrity," he said.

Self-repairing glass could one day be used in the armored windscreens of military vehicles -- allowing passengers to drive away from the site of conflict with clear vision -- or in smartphone screens, although in practice, there may not be much demand for a long-life mobile phone.

"We've proved that you could do it, but the trouble with mobile phones is they only have a life of about six months anyway," he said. "It's the sexiness of the next phone that dictates their life."

The creation of materials that were able to heal over puncture wounds -- such as a blast hole in a plane fuselage -- remains far off, although there's some idea how you might do that using polymers, Bond says.

"That's a logical step from the simple idea we've started with, because that's what nature does," he said. "This is the beginning of the concept of allowing materials to recover fully."